The invention relates to a gripper for retaining sheet-like articles, in particular flexible articles such as printed products containing one or more sheets, having two gripper legs which can be pivoted relative to one another and, in a closed position, subject the retained article to a clamping action, and having an actuating device which acts on at least one of the gripper legs in order to produce a pivoting movement of the two gripper legs relative to one another, it being possible for the actuating device to be moved in a translatory manner for the changeover between an open position and the closed position of the gripper legs.
Such grippers are used, in particular, in conveying apparatus for the individual transportation of articles. For example, these articles may be various printer products which are retained in a hanging position by grippers guided along a transporting path.
A gripper of the type mentioned in the introduction is known from European Patent Application EP 0 767 125 A1. The gripper disclosed therein has two gripper legs which are retained in the closed position by a closing device with two clamping bodies. Pivoting or translatory movement of the closing device allows the gripper legs to be released and to pivot to their open position.
This known gripper has the disadvantage that the gripper legs, which can be pivoted in a freely movable manner, actually only pivot into a definite open position when an additional element, for example a compression spring which subjects the clamp jaws to a continuous spreading force, is provided.
It is an object of the invention to provide a gripper of the type mentioned in the introduction which, along with a straightforward mechanical construction, can execute a precise changeover between the closed position and open position. The gripper is intended to make it possible for the article to be retained in a secure manner and for the opening and closing movements to be controlled in a straightforward manner.
The object is achieved according to the invention in that the actuating device has at least one sliding part, it being possible, by way of the translatory movement of the latter, for at least one gripper leg to be subjected to force either in the direction of the open position or in the direction of the closed position.
Translatory movement of the sliding part in the context of the invention is to be understood as any movement relative to the gripper legs along a straight line or curve.
The at least one gripper leg may thus be subjected to force by means of the sliding part. By corresponding translatory movement of the sliding part, it is possible, for the active control both of the closing movement and of the opening movement of the gripper leg, for the direction and magnitude of the force to be determined directly without further auxiliary means such as additional mechanical elements being necessary for this purpose.
The possibility of actively moving the gripper legs in two opposite directions allows controlled closing and opening movements, for example in order to allow an article, with simultaneous movement of the gripper, to drop at a precise time and location.
Since, in the case of the gripper according to the invention, an opening and closing movement can be produced by a single sliding part, of which the structural configuration is not subject to any stringent requirements, it is possible for the gripper to be designed easily and cost-effectively in a manner which particularly reduces weight, the materials used and the amount of space required.
In comparison with known grippers in which spreading stress which acts permanently on the legs is provided in order to force the legs passively to open, the gripper according to the invention has the advantage that the legs may be actively caused to execute any desired pivoting movement and, at the same time, may be mounted in a freely pivotable manner without such spreading stress, with the result that, during the active pivoting movement of the legs, there is no need for any additional force to be applied in order to overcome such spreading stress.
Finally, the forces which are necessary for the translatory movement of the sliding part may advantageously be transmitted to the sliding part symmetrically in relation to the axes of symmetry of the gripper, with the result that there is no need to take any particular measures in order to stabilize the gripper against possible tilting movements.
In a preferred embodiment, the sliding part of the gripper has a spreading element which, in order to cause an opening movement or stabilize at least one gripper leg, can subject the latter to a spreading force. In particular, the spreading element may be arranged between the two gripper legs and may subject the two gripper legs simultaneously to the spreading force.
It is also preferred if the sliding part has one or two closing elements by means of which a respectively associated gripper leg can be subjected to a closing force in order to cause said gripper leg to execute a closing movement or to stabilize the same in a certain position.
The gripper legs may have at least one latching depression in which the respectively associated closing element can be latched in a certain opening position of the gripper legs, for example the closed position. This makes it possible to maintain this position without the respective gripper leg having to be actively subjected to force, for example, by being continuously subjected to the action of force or by translatory movement of the sliding part.
It is preferred if that section of the spreading element or of the closing element which is directed toward a gripper leg is designed as a flat surface. In this case, force is transmitted particularly homogeneously from the sliding part to a gripper leg, which is likewise designed as a flat surface. The force-transmission surface area of the closing element preferably extends along the entire width of the associated gripper leg. The forcetransmission surface area of the spreading element may be designed as at least one nose which extends along merely the border of the respectively associated gripper leg.
It has proven to be particularly effective and straightforward for the gripper leg to be subjected to the action of force by the sliding part and the guidance of the sliding part if the sliding part is moved along or parallel to an axis or plane in relation to which the two gripper legs are arranged symmetrically, in particular in their closed position. This is because, in this case, transverse forces are avoided, with the result that mechanical configuration of the gripper and of the sliding-part guide means is also simplified.
In a preferred embodiment of the gripper, the actuating device has precisely one sliding part with essentially two openings, through which in each case one gripper leg runs. This means that the two gripper legs can be simultaneously subjected to the action of force, and moved, solely by the translatory movement of the single sliding part.
In a further embodiment of the invention, it is possible for the actuating device to have precisely two sliding parts with in each case one opening, in each case one gripper leg running through each opening. In this case, the two sliding parts and thus the respective opening position of the corresponding legs can be respectively actuated and influenced with one another or independently of one another. Preferably provided in this embodiment is a guide means which ensures translatory movement of the two sliding parts along mutually parallel paths.
Finally, in a further embodiment of the gripper according to the invention, it is possible for the actuating device to have precisely one sliding part with an opening, through which merely one of the two gripper legs runs. If it is just this gripper leg which is suspended pivotably in a freely movable manner, and the other gripper leg assumes an essentially fixed position, it is possible for the sliding part and thus also the pivotable gripper leg to be actuated between the closed position and the open position of the gripper, with the simplified mechanical configuration.
It is possible, in the case of the abovementioned embodiments of the invention, for the two gripper legs to be designed as separate parts or in one piece. For the purpose of securely gripping and retaining sheet-like articles, it is possible for the gripper legs to be designed as gripper jaws in the form of a flat surface or of a flat-surface outline, the flat-surface sides of the two gripper jaws being directed essentially toward one another.
In particular in the case of a flat-surface configuration of the gripper legs as gripper jaws, it is advantageous if the abovementioned openings provided in the sliding part or parts are of slit-like design, and, as appropriate, run essentially parallel to one another. In this case, it is possible for the respective sliding part to butt closely against the corresponding gripper leg along a considerable length. This makes possible a particularly effective, homogeneous and quick force fit between the sliding part and the gripper leg.
In the case of the gripper according to the invention, the sliding part may enclose a gripper leg in the form of a ring. Alternatively, two mutually opposite sides of a gripper leg may also be subjected to the action of force by the sliding part in that the sliding part has an essentially U-shaped cross section and the gripper leg is arranged between the two U-legs of the sliding part. In this context, it is also possible to have an indent which is open on one side as one of the abovedescribed openings.
The two gripper legs may each be arranged in a freely movable manner, with the result that they may be pivoted independently of one another in each case without any substantial opposing force. For example, they may be mounted on a common pivot pin or on a dedicated pivot pin in each case. Alternatively, the two legs may also be fastened with one another such that, without the external action of force, they assume a defined rest position relative to one another which corresponds, for example, to the open position, the closed position or some other position.
The translatory movement of the sliding part may be controlled and/or produced in a known manner, for example by the provision, on one or both ends of the sliding part, of guide rollers which, during movement of the gripper, run along opening or closing guides. It is also possible for the gripper according to the invention to be equipped in a known manner with a suspension device for fastening on a transporting path.
The invention also covers a conveying apparatus which has a multiplicity of the grippers according to the invention for the individual transportation of articles.
Further preferred embodiments of the invention are described in the subclaims.